Comment 5 for bug 1619679

Naturally, after the failed build, Wifi does not work. Rebooting with the previous kernel (3.19.0-68-generic #76~14.04.1-Ubuntu) restores Wifi.

After a bit of googling, I found someone suggesting that kernel build errors may be due to using an old version of gcc. This sounded good, so I installed gcc-4.9 as per

http://askubuntu.com/questions/466651/how-do-i-use-the-latest-gcc-on-ubuntu

Next I uninstalled and re-installed bcmwl-kernel-source. It took a while to build the module, but after that booting using kernel 4.4 brought back Wifi.